Soil Stabilisation

Benefits of using Ardula and Sussex Stabilisation Group for In situ soil stabilisation

With recycled aggregate becoming increasingly difficult to source, surplus soils on site can be modified to form recognised capping alternatives. A specified 6F capping product can be replaced with a specification for highways works 9D, with improved performance and reduced risk of impact of moisture content of the subgrade to be constructed upon.

By combining with Sussex Stabilisation Group, Ardula can now offer a unique service, linking on site soil re-use with transportation of materials to other sites, by deploying it's mobile treatment permits to provide not only cost effective on site treatment, but environmentally compliant transportation and re-use of treated materials

Soil Stabilisation - a simple explanation

Methods of soil stabilisation using binders

1. Modification is the addition of lime to unsuitable (i.e too wet) or marginal soil to dry the soil to allow for placement as a subgrade improvement or capping layer  
2. Lime Stabilisation is the treatment of soils to achieve a long term increase in strength due to cementitious reactions activated by lime  
3. Cement Stabilisation is the addition of further cementitious binders to increase the platform to greater strengths

Typical applications

• Improving wet materials for engineered fill 
• Sub-base replacement for roads & foundations 
• Improving capping layer performance 
• Processing sub-base for roads & floor slabs 
• Constructing pile mats & engineered platforms 
• Treating contaminated land 

The following information is extracted from the Britpave Guidance (updated 2019), and provides and overview of why soil stabilisation should be considered, and what the benefits are

What and Why?

Both soil improvement and soil stabilisation consist of adding binders in-situ to improve the soil performance as an alternative to ‘dig and dump’. They have a long track record and are both cost effective and sustainable. The benefits include reduced aggregate importing and off-site disposal and the attendant reduced vehicle movement. Soil improvement is also often used to gain rapid access to wet sites in a single operation.
Soil improvement and soil stabilisation can be used for fills, foundations, subgrade improvement, slope repairs, working platforms and hardstandings.

Soil improvement

Soil improvement is generally achieved by adding binders. It is sometimes termed soil modification in the literature.
The benefits Soil improvement is used to address handling or compacting problems resulting from high plasticity or high water content. Such soils can be improved by mixing with lime. Adding lime to clay provides three important benefits:

• Breaking down clay inter-particle cohesion,

• Reduced plasticity,

• Moisture content reduction.

This improves the soil’s ability to be:

• handled by conventional earthmoving plant;

• satisfactorily compacted in layers, especially when the moisture content is wet of optimum;

• trafficked and provide a working platform for subsequent layers; • prepared for further treatment.

Soil improvement should be carried out in accordance with the following: • BS EN 16907 Earthworks Part 4: Soil treatment with lime and / or hydraulic binders • Series 600 Specification for Highway Works, Earthworks • Specific project specification(s)

Lime is the only binder that breaks down clay inter-particle cohesion. This makes soil improvement a necessary first stage in cohesive soil stabilisation where more than one binder is to be used. A mellowing period may be required to allow the lime to break down the clay to achieve both adequate pulverisation and to allow full activation of secondary binders if used. Historically, a mellowing period of between 24 to 72 hours was specified. However, with the efficiency in mixing that modern stabilisation plant provides this can be much shorter depending on the soil properties and the secondary binders used.

Soil stabilisation

Whilst soil improvement is beneficial for conditioning soils there may be limited strength increase. To improve strength it is necessary to go to a second stage termed soil stabilisation. 
Soil stabilisation should be carried out in accordance with the following:

• BS EN 16907 Earthworks Part 4: Soil treatment with lime and / or hydraulic binders

• Series 600 Specification for Highway Works, Earthworks

• BS EN 14227 for pavement foundations

• Series 800 Specification for Highway Works, unbound, cement and other hydraulically bound mixtures

• Specific project specification Informative information regarding soil treatment equipment types, sequence and processes are provided in BS 16907 Earthworks Par4: Annexes H and I.

The benefits of soil improvement and soil stabilisation are proven civil engineering techniques. Treating materials insitu is efficient, cost effective and offers a number of benefits

Engineered Material

Soil stabilisation results in engineered materials that provide: • improved static load resistance • improved resilient behaviour (stiffness) under dynamic loads • reduced permeability • improved freeze-thaw resistance

The keys to success are using the correct binder and ensuring compaction using good earthworks practice. Reduced costs In-situ treatment of soil can be more cost-effective than traditional ‘dig and dump’ methods which incur transport plus importation and disposal costs.

Reduced programme

Soil stabilisation can reduce construction programme times by minimising site preparation and designing out imported materials and unacceptable material disposal. Soil improvement allows wet ground to be dried and strengthened within a very short timescale. This permits working in wet conditions and allows work to restart promptly following rainfall. For the construction programme benefits to be fully realised, longer lead-in time is needed during the design stage for ground investigation and mix design. 

Improved Sustainability

Soil improvement and stabilisation offer significant environmental benefits over traditional ‘dig and dump’. Improvement and stabilisation turn unacceptable soils into engineered material. They avoid offsite disposal and importing acceptable fill, which often comprise virgin aggregates. There is no removal of waste materials and corresponding importation of aggregates. This reduces lorry movements on the local road network and therefore greatly reduces traffic congestion and pollution.

The delivery of the above benefits relies upon strict adherence to the relevant technical specifications and standards, plus the full implementation of good practice by a specialist contractor.